Filter media including a waved filtration layer

ABSTRACT

Filter media including a waved filtration layer are described herein. The filtration layer may be held in a waved configuration by a support layer. In some cases, the filtration layer may have a combination of characteristics (e.g., mean flow pore size, basis weight, amongst others) that can lead to enhanced filtration performance (e.g., reduced air permeability decrease), in particular, in high humidity environments. The filter media may be used to form a variety of filter elements for use in various applications.

FIELD OF THE INVENTION

The present invention relates to filtration and, more particularly, tofilter media that include a waved filtration layer.

BACKGROUND

Filter media can be used to remove contamination in a variety ofapplications. In general, filter media include one or more fiber webs.The fiber web provides a porous structure that permits fluid (e.g., air)to flow through the web. Contaminant particles contained within thefluid may be trapped on the fiber web. Fiber web characteristics (e.g.,pore size, fiber dimensions, fiber composition, basis weight, amongstothers) affect filtration performance of the media. Although differenttypes of filter media are available, improvements are needed.

SUMMARY

In one aspect, a filter media is provided. The filter media comprises afiber filtration layer and a support layer that holds the fiberfiltration layer in a waved configuration and maintains separation ofpeaks and troughs of adjacent waves of the fiber filtration layer. Thefiber filtration layer has a mean flow pore size of at least about 11.5microns. The filter media has a minimum DEHS particle filtrationefficiency of at least about 25%.

In another aspect, a filter media is provided. The filter mediacomprises a fiber filtration layer and a support layer that holds thefiber filtration layer in a waved configuration and maintains separationof peaks and troughs of adjacent waves of the fiber filtration layer.The fiber filtration layer in the waved configuration is formed from afiber layer having a planar configuration and a transition salt load ofat least about 2.0 gsm. The filter media has a minimum DEHS particlefiltration efficiency of at least about 25%.

Other aspects and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view illustration of one embodiment of a filter media;

FIG. 1B is a side view illustration of another embodiment of a filtermedia;

FIG. 1C is a side view illustration of one layer of the filter media ofFIG. 1A;

FIG. 2A is a plot showing resistance pressure versus salt loading forvarious fiber filtration layers;

FIG. 2B is a plot showing transition salt loading versus mean flow poresize for various fiber filtration layers;

FIG. 2C is a plot showing cake pressure slope versus mean flow pore sizefor various fiber filtration layers;

FIG. 3A is a plot the specific natural log of penetration (i.e., thenatural log of the penetration divided by the basis weight) versus meanflow pore size for various fiber filtration layers;

FIG. 3B is a plot showing basis weight versus mean flow pore size forvarious fiber filtration layers;

FIG. 4 is a plot showing the percentage difference between the maximumair permeability minus the minimum air permeability value expressed as apercentage of the maximum value versus mean flow pore size for variousfilter media in a humid environment.

DETAILED DESCRIPTION

Filter media including a waved filtration layer are described herein.The filtration layer may be held in a waved configuration by a supportlayer. As described further below, the filtration layer may have acombination of characteristics (e.g., mean flow pore size, basis weight,amongst others) that can lead to enhanced filtration performance (e.g.,efficiency), in particular, in high humidity environments. The filtermedia may be used to form a variety of filter elements for use invarious applications.

Media

In general, various filter media are provided having at least onefiltration (e.g., fibrous) layer that is held in a waved or curvilinearconfiguration by one or more additional support layers (e.g., fibrous).As a result of the waved configuration, the filter media has anincreased surface area which can result in improved filtrationproperties. The filter media can include various layers, and only someor all of the layers can be waved.

FIG. 1A illustrates one exemplary embodiment of a filter media 10 havingat least one filtration layer and at least one support layer that holdsthe filtration layer in a waved configuration to maintain separation ofpeaks and troughs of adjacent waves of the filtration layer. In theillustrated embodiment, the filter media 10 includes a fiber filtrationlayer (e.g., a fine fiber filtration layer) 12, a first, downstreamsupport layer 14, and a second, upstream support layer 16 disposed onopposite sides of the fiber filtration layer 12. The support layers 14,16 can help maintain the fiber filtration layer 12, and optionally anyadditional filtration layers, in the waved configuration. While twosupport layers 14, 16 are shown, the filter media 10 need not includeboth support layers. Where only one support layer is provided, thesupport layer can be disposed upstream or downstream of the filtrationlayer(s).

The filter media 10 can also optionally include one or more outer orcover layers located on the upstream-most and/or downstream-most sidesof the filter media 10. FIG. 1A illustrates a top layer 18 disposed onthe upstream side of the filter media 10 to function, for example, as anupstream dust holding layer. The top layer 18 can also function as anaesthetic layer, which will be discussed in more detail below. Thelayers in the illustrated embodiment are arranged so that the top layer18 is disposed on the air entering side, labeled I, the second supportlayer 16 is just downstream of the top layer 18, the fiber filtrationlayer 12 is disposed just downstream of the second support layer 16, andthe first support layer 14 is disposed downstream of the first layer 12on the air outflow side, labeled O. The direction of air flow, i.e.,from air entering I to air outflow O, is indicated by the arrows markedwith reference A.

The outer or cover layer can alternatively or additionally be a bottomlayer disposed on the downstream side of the filter media 10 to functionas a strengthening component that provides structural integrity to thefilter media 10 to help maintain the waved configuration. The outer orcover layer(s) can also function to offer abrasion resistance. FIG. 1Billustrates another embodiment of a filter media 10B that is similar tofilter media 10 of FIG. 1B. In this embodiment, the filter media 10Bdoes not include a top layer, but rather has a fiber filtration layer12B, a first support layer 14B disposed just downstream of the fiberfiltration layer 12B, a second support layer 16B disposed just upstreamof the fiber filtration layer 12B on the air entering side I, and abottom layer 18B disposed just downstream of the first support layer 14Bon the air exiting side O. Furthermore, as shown in the exemplaryembodiments of FIGS. 1A and 1B, the outer or cover layer(s) can have atopography different from the topographies of the fiber filtration layerand/or any support layers. For example, in either a pleated ornon-pleated configuration, the outer or cover layer(s) may be non-waved(e.g., substantially planar), whereas the fiber filtration layer and/orany support layers may have a waved configuration. A person skilled inthe art will appreciate that a variety of other configurations arepossible, and that the filter media can include any number of layers invarious arrangements.

Fiber Filtration Layer

As indicated above, in an exemplary embodiment the filter media 10includes at least one fiber filtration layer 12, which may optionally behydrophobic or hydrophilic. In an exemplary embodiment, a singlefiltration layer 12 formed from fine fibers is used, however the filtermedia 10 can include any number of additional filtration layers disposedbetween the downstream support layer and the upstream support layer,adjacent to the fiber filtration layer 12, or disposed elsewhere withinthe filter media. While not shown, the additional filtration layer(s)can be maintained in a waved configuration with the fiber filtrationlayer 12. In certain exemplary embodiment the filter media 10 caninclude one or more additional filtration layers disposed upstream ofthe fiber filtration layer 12. The additional filtration layer(s) can beformed from fine fibers, or can be formed from fibers having an averagefiber diameter that is greater than an average fiber diameter of thefibers that form the fiber filtration layer 12.

The fiber filtration layer may be designed to have a particular meanflow pore size. Advantageously, fiber filtration layers having a meanflow pore size of 11.5 microns or greater may, in some embodiments, haveincreased NaCl loading, improved high humidity performance, and/orsmaller reduction in air permeability after NaCl loading as compared tofiber filtration layers having smaller mean flow pore sizes. In someembodiments, the fiber filtration layer has a mean flow pore size of atleast about 11.5 microns, at least about 13 microns, at least about 15microns, at least about 16 microns, at least about 20 microns, at leastabout 25 microns, at least about 30 microns, at least about 35 microns,or at least about 40 microns. In certain embodiments, the fiberfiltration layer has a mean flow pore size less than or equal to about45 microns, less than or equal to about 40 microns, less than or equalto about 35 microns, less than or equal to about 30 microns, less thanor equal to about 25 microns, less than or equal to about 20 microns,less than or equal to about 16 microns, less than or equal to about 15microns, or less than or equal to about 13 microns. Combinations of theabove referenced ranges are also possible (e.g., between about 11.5microns and about 45 microns, between about 11.5 microns and about 25microns, between about 11.5 microns and about 16 microns). Other rangesare also possible including, in some embodiments, less than 11.5microns.

As used herein, the mean flow pore size refers to the mean flow poresize measured by a capillary flow porometer (e.g., Model CFP-34RTF8A-X-6 manufactured by Porous Materials, Inc.) in accordance with theASTM F316-03 standard using a 1,1,2,3,3,3-hexafluoropropene low surfacetension fluid. The mean flow pore size of a fiber filtration layer maybe designed by selecting an average fiber diameter, basis weight, and/orthickness of the layer as known to those of ordinary skill in the art.In some cases, mean flow pore size may be designed by adjustingprocessing parameters such as air flow rate and/or temperature duringmanufacturing (e.g., using meltblowing techniques) of the fiberfiltration layer. In some embodiments, a combination of filtrationlayers may have a mean flow pore size in one or more of theabove-referenced ranges. Additionally, in embodiments in which more thanone filtration layers are present in a media, each filtration layer mayhave a mean flow pore size having one or more of the above-referencedranges.

The basis weight of the fiber filtration layer can be designed byadjusting processing parameters such as the number of fibers included inthe filtration layer. In some embodiments, the basis weight of the fiberfiltration layer may be greater than or equal to about 10 g/m² (e.g.,greater than or equal to about 12 g/m², greater than or equal to about14 g/m², greater than or equal to about 15 g/m², greater than or equalto about 16 g/m², greater than or equal to about 18 g/m², greater thanor equal to about 20 g/m², greater than or equal to about 25 g/m²,greater than or equal to about 30 g/m², or greater than or equal toabout 35 g/m²). In some cases, the basis weight of the fiber filtrationlayer may be less than or equal to about 40 g/m² (e.g., less than orequal to about 40 g/m², less than or equal to about 35 g/m², less thanor equal to about 30 g/m², less than or equal to about 25 g/m², lessthan or equal to about 20 g/m², less than or equal to about 18 g/m²,less than or equal to about 16 g/m², less than or equal to about 15g/m², less than or equal to about 14 g/m², or less than or equal toabout 12 g/m²). Combinations of the above-referenced ranges are alsopossible (e.g., a basis weight of greater than or equal to about 10 g/m²and less than or equal to about 40 g/m², or greater than or equal toabout 14 and less than or equal to about 20 g/m²). Other ranges are alsopossible. In some embodiments, a combination of filtration layers mayhave a combined basis weight in one or more of the above-referencedranges. As determined herein, the basis weight of the filtration layeris measured according to the Edana WSP 130.1 Standard. Additionally, inembodiments in which more than one filtration layers are present in amedia, each filtration layer may have a basis weight having one or moreof the above-referenced ranges.

The basis weight and/or mean flow pore size may be tuned such that thefiber filtration layer has a desired minimum DEHS(diethyl-hexyl-sebacate) particle filtration efficiency. In some cases,the basis weight of the fiber filtration layer and/or the mean flow poresize of the fiber filtration layer may be increased or decreased, suchthat the fiber filtration layer has a particular minimum DEHS particlefiltration efficiency (e.g., a minimum DEHS particle filtrationefficiency of at least about 25%). For example, in some embodiments, thebasis weight may be adjusted (e.g., increased) for a fiber filtrationlayer having a mean flow pore size of at least about 11.5 microns suchthat the fiber filtration layer has a minimum DEHS particle filtrationefficiency of at least about 25%. In some embodiments and as describedfurther in Example 1, the relationship between the basis weight, meanflow pore size, and efficiency of the fiber filtration layer may beexpressed as:

${BW} > \frac{{- {MP}^{a\;}}{\ln\left( {1 - E} \right)}}{b}$wherein BW is the basis weight (in grams per square meter) of the fiberfiltration layer, MP is the mean pore size (in microns) of the fiberfiltration layer, a and b are coefficients, and E is the minimum DEHSparticle filtration efficiency (expressed as a fraction) of the fiberfiltration layer. In some embodiments, a is 2 and b is 6.5. In someembodiments, a is a number greater than or equal to 2 and less than orequal to 2.3, and b is a number greater than or equal to 6.5 and lessthan or equal to about 8. For example, in some other embodiments, a is2, 2.1, 2.25, or 2.28 and b is 6.5, 7, 7.5, or 8. In some cases, theparameters may be selected (e.g., basis weight) to obtain a particularminimum DEHS particle filtration efficiency (e.g., a minimum DEHSparticle filtration efficiency of at least about 0.25 (i.e., 25%) or atleast about 0.35 (i.e., 35%)) for a given mean flow pore size. Forexample, in some cases, the fiber filtration layer has a particularminimum DEHS particle filtration efficiency (e.g., at least about 25% orat least about 35%) and a particular mean flow pore size (e.g., at leastabout 11.5 microns), and the basis weight may be designed to be at leastabout 8.76 g/m², when a is 2 and b is 6.5. Without wishing to be boundby theory, the equation above demonstrates a relationship between basisweight, mean flow pore size, and efficiency of a fiber filtration layerwhich can be used to design fiber filtration layer(s) that providedesirable performance under humid conditions, including a smallerdecrease in air permeability in humid environments as compared tocertain traditional fiber filtration layers. Air permeability in humidenvironments is described in more detail below.

The fiber filtration layers and/or filter media described herein (e.g.,having a mean flow pore size of at least about 11.5 microns) may have awide range of minimum DEHS particle filtration efficiencies. In someembodiments, the minimum DEHS particle filtration efficiency of thefiber filtration layer and/or filter media is between about 25% andabout 75%, between about 30% and 75%, or between about 35% and about55%. In some embodiments, the fiber filtration layer and/or filter mediahas a minimum DEHS particle filtration efficiency of greater than orequal to about 25%, greater than or equal to about 30%, greater than orequal to about 35%, greater than or equal to about 45%, greater than orequal to about 55%, or greater than or equal to about 65%. Other minimumDEHS particle filtration efficiencies are also possible. In someembodiments, the fiber filtration layer and/or filter media has aminimum DEHS particle filtration efficiency of less than or equal to75%, less than or equal to 65%, less than or equal to 55%, or less thanor equal to 45%. In some embodiments, a combination of fiber filtrationlayers may have a minimum DEHS particle filtration efficiency in one ormore of the above-referenced ranges. In some embodiments, the minimumDEHS particle efficiency of the filter media may be greater than that ofthe fiber filtration layer, because additional layers added to the media(e.g., an outer or cover layer) may help to trap particles, therebyincreasing the minimum DEHS particle of the overall filter media.

In some embodiments, the fiber filtration layers and/or filter mediadescribed herein (e.g., having a mean flow pore size of at least about11.5 microns) may have a wide range of average DEHS particle filtrationefficiencies. In some embodiments, the average DEHS efficiency of thefiber filtration layer and/or filter media is greater than or equal toabout 25%, greater than or equal to about 30%, greater than or equal toabout 35%, greater than or equal to about 40%, greater than or equal toabout 45%, greater than or equal to about 50%, greater than or equal toabout 55%, greater than or equal to about 60%, greater than or equal toabout 65%, greater than or equal to about 70%, greater than or equal toabout 75%, or greater than or equal to about 80%. Other efficiencies arealso possible. In some embodiments, the fiber filtration layer and/orfilter media has an average DEHS efficiency of less than or equal to99.9%, less than or equal to 99.8%, less than or equal to 99.7%, lessthan or equal to 99.5%, less than or equal to 99%, less than or equal to98%, less than or equal to 95%, less than or equal to 90%, less than orequal to 85%, less than or equal to 80%, less than or equal to 70%, lessthan or equal to 60%, or less than or equal to 50%. In some embodiments,the average DEHS particle efficiency of the filter media may be greaterthan that of the fiber filtration layer, because additional layers addedto the media (e.g., an outer or cover layer) may help to trap particles,thereby increasing the average DEHS particle efficiency of the overallfilter media.

The minimum and average DEHS particle filtration efficiency of afiltration layer or a filter media, as referred to herein, are testedfollowing the EN779-2012 standard and using 0.4 micron or larger. Thetesting uses an air flow of 0.944 m³/s. The testing begins by initiallymeasuring the pressure drop and DEHS particle efficiency of a sample.The testing then involves progressively loading the sample with standardtest dust (ANSI/ASHRAE 52.2) in 30 g increments and measuring thepressure drop and DEHS particle efficiency after each loading incrementuntil a pressure drop of 450 Pa or greater is reached at which point thetesting is complete. The minimum DEHS particle filtration efficiency, asused herein, refers to the lowest DEHS particle efficiency obtainedthroughout the test. The average DEHS particle filtration efficiency, asused herein, is determined as the average of the DEHS particleefficiencies obtained throughout the test (including the DEHS particleefficiency measured initially prior to standard test dust loading andthe DEHS particle efficiencies at all loading levels including theparticle DEHS efficiency at the maximum test pressure of 450 Pa orgreater).

As described herein, the fiber filtration layers (e.g., having a meanflow pore size greater than about 11.5 microns) and/or filter media mayadvantageously have improved performance (e.g., reduced air permeabilitydecrease) in high humidity environments as compared to certaintraditional fiber filtration layers (e.g., having mean flow pore sizesless than about 11.5 microns). Without wishing to be bound by theory,improved humidity performance may be generally correlated with increasedtransition salt loading of a fiber filtration layer. In some cases,transition salt loading may be measured using a NaCl (sodium chloride)challenge (or NaCl loading), which employs an automated filter testingunit (e.g., 8130 CertiTest™ from TSI, Inc.) equipped with a sodiumchloride generator. The average particle size created by the saltparticle generator is about 0.3 micron mass mean diameter. Theinstrument measures a pressure drop across the filtration layer and/orfilter media and the resultant penetration value on an instantaneousbasis. The testing unit can be run in a continuous mode with onepressure drop/penetration reading approximately every minute. The NaClparticles at a concentration of 23 mg NaCl/m³ air are continuouslyloaded onto a 100 cm² sample at a flow rate of 5.3 cm/s. The samples arecontinuously loaded until 1% (or lower) penetration is achieved.Penetration, often expressed as a percentage, is defined as follows:Pen=C/C ₀where C is the particle concentration after passage through the filterand C₀ is the particle concentration before passage through the filter.

In some embodiments, the fiber filtration layer and/or the filter mediahas a transition salt load of at least about 2.0 gsm (grams per squaremeter). Transition salt load may be determined by performing NaClloading as described above on a planar fiber filtration layer or on thefilter media as a whole, and plotting the resistance pressure (in mmH₂O) as a function of NaCl load (gsm (i.e., grams per square meter)).Referring now to FIG. 2A, an initial depth loading line is calculated byfitting a simple linear regression line to the initial ten minute region(i.e., initial ten consecutive data points) of the NaCl loading curve(i.e., resistance pressure versus NaCl load) which begins with the firstreading taken at one minute after the onset of testing. A cake loadingline (see FIG. 2A) is calculated by fitting a simple linear regressionline to ten consecutive data points of the NaCl loading curve, whereinthe first through tenth data points are selected such that penetrationof the fiber filtration layer and/or filter media is less than 1% andthe eleventh data point (not included in the simple linear regressionfit) is greater than or equal to 1% penetration (e.g., drawn through 10data points preceding and including the one at which measuredpenetration drops below 1%). The transition salt load described hereinis defined as the value of NaCl load (in grams) per unit area (in squaremeters) of the fiber filtration layer at the intersection of the initialdepth loading line and the cake loading line.

In some embodiments, the transition salt load of a planar fiberfiltration media is at least about 2.0 gsm, at least about 2.5 gsm, atleast about 3.0 gsm, at least about 3.5 gsm, at least about 4.0 gsm, orat least about 5.0 gsm. In some embodiments, the transition salt load isless than or equal to about 10.0 gsm, less than or equal to about 5.0gsm, less than or equal to about 4.0 gsm, less than or equal to about3.5 gsm, less than or equal to about 3.0 gsm, or less than or equal toabout 2.5 gsm. Combinations of the above referenced ranges are alsopossible (e.g., between about 2.0 gsm and about 10.0 gsm). The fiberfiltration layers and filter media described herein generally haveincreased transition salt loads as compared to traditional filtrationlayers and filter media which, generally, corresponds to lowerresistance pressures for an equivalent amount of NaCl loading.

The slope of the cake loading line, described herein, may have aparticular value. In some embodiments, the slope of the cake loadingline of the fiber filtration layer may be less than or equal to about7.5 mm H₂O/gsm salt load, less than or equal to about 7 mm H₂O/gsm saltload, less than or equal to about 6 mm H₂O/gsm salt load, less than orequal to about 5.5 mm H₂O/gsm salt load, less than or equal to about 5mm H₂O/gsm salt load, less than or equal to about 4.5 mm H₂O/gsm saltload, less than or equal to about 4 mm H₂O/gsm salt load, or less thanor equal to about 3.5 mm H₂O/gsm salt load. In some embodiments, theslope of the cake loading line of the fiber filtration layer may begreater than or equal to 0 mm H₂O/gsm salt load, greater than or equalto about 1 mm H₂O/gsm salt load, greater than or equal to about 2 mmH₂O/gsm salt load, greater than or equal to about 3 mm H₂O/gsm saltload, greater than or equal to about 4 mm H₂O/gsm salt load, greaterthan or equal to about 4.5 mm H₂O/gsm salt load, greater than or equalto about 5 mm H₂O/gsm salt load, greater than or equal to about 5.5 mmH₂O/gsm salt load, or greater than or equal to about 6 mm H₂O/gsm saltload, or greater than or equal to about 7 mm H₂O/gsm salt load.Combinations of the above referenced ranges are also possible (e.g.,between 0 mm H₂O/gsm salt load and about 7 mm H₂O/gsm salt load, between1 mm H₂O/gsm salt load and about 7 mm H₂O/gsm salt load, between about 3mm H₂O/gsm salt load and about 6 mm H₂O/gsm salt load, between about 5mm H₂O/gsm salt load and about 6 mm H₂O/gsm salt load). Other ranges arealso possible.

Advantageously, in some embodiments, the fiber filtration layersdescribed herein (e.g., having a mean flow pore size greater than about11.5 microns) and/or filter media may have relatively lower decrease inair permeability in humid environments as compared to certaintraditional fiber filtration layers (e.g., having a mean flow pore sizeless than about 11.5 microns) and/or filter media. In some embodiments,the percent decrease in air permeability after humidity loading is lessthan or equal to about 50%, less than or equal to about 45%, less thanor equal to about 44%, less than or equal to about 42%, less than orequal to about 40%, less than or equal to about 35%, less than or equalto about 30%, or less than or equal to about 25%. In certainembodiments, the percent decrease in air permeability after humidityloading is at least about 25%, at least about 35%, at least about 40%,at least about 42%, at least about 44%, or at least about 45%.Combinations of the above-referenced ranges are also possible (e.g., adecrease in air permeability after humidity loading of between about 35%and 50%, between about 42% and about 45%, between about 42% and about50%). Other ranges are also possible.

Air permeability after humidity loading, as referred to herein, isdetermined by performing a humidity challenge after loading a 100 cm²sample with NaCl aerosol (23 mg NaCL/m³ air) of approximately 0.3 micronparticle for 30 minutes using an automated filter testing unit (e.g.,TSI 8130 CertiTest™ from TSI, Inc.) equipped with a sodium chloridegenerator. Samples (e.g., filter media in a waved configurationincluding a fiber filtration layer and a support layer) are loaded at aface velocity of 14.1 cm/sec for 30 minutes. Once loaded with NaCl, thesamples are placed into a sample holder connected to an Frazier airpermeability machine and enclosed in a chamber containing a steamgenerator to generate humidity. A hygrometer probe is inserted into thebox to measure the temperature and humidity within the chamber. At thebeginning of the test the relative humidity in the chamber is 50% andthe test is conducted by taking initial air permeability readings atpressure drop of 0.5″ water column, after which the steam generator isturned on and air permeability and humidity readings are taken every 30seconds. Once humidity reaches 90%, the readings are continued forapproximately 12 minutes, after which the steam generator is turned off.Readings are continued until the air permeability stabilizes. Thepercent decrease in air permeability after humidity loading is thedifference between the maximum air permeability minus the minimum airpermeability value expressed as a percentage of the maximum value.

In some cases, the fiber filtration layer may have a particularsolidity. Solidity, as used herein, generally refers the basis weight ofthe fiber filtration layer divided by the average density of the fiberstimes the uncompressed thickness of the fiber filtration layer (i.e.BW/(ρ*t)), where BW is the basis weight, ρ is the density, and t is theuncompressed thickness). Uncompressed thickness, as used herein, refersto the thickness of the fiber filtration layer as determined from ameasurement of the thickness of the fiber filtration layer with amicrometer under a series of different loads) and extrapolating todetermine the thickness under zero loading. In some embodiments, thefiber filtration layer has a solidity of at least about 1%, at leastabout 2%, at least about 2.5%, at least about 5%, at least about 10%, atleast about 13%, or at least about 15%. In certain embodiments, thefiber filtration layer has a solidity of less than or equal to about20%, less than or equal to about 15%, less than or equal to about 13%,less than or equal to about 10%, less than or equal to about 5%, lessthan or equal to about 4%, less than or equal to about 3.5%, less thanor equal to 3%, less than or equal to about 2.5%, or less than or equalto about 2%. Combinations of the above-referenced ranges are alsopossible (e.g., between about 1% and about 20%, between about 2.5% andabout 13%, between about 5% and about 20%). Other ranges are alsopossible.

In some embodiments, the fiber filtration layer may have a particularsurface area. In some cases, the surface area of the fiber filtrationlayer may be between about 0.8 square meters per gram and about 2.5square meters per gram. For example, the surface area may be betweenabout 1.2 square meters per gram and about 1.6 square meters per gram.Surface area can be determined by any suitable method known in the artincluding, for example, BET gas adsorption.

The fiber filtration layer 12 can be formed from a variety of fibers,but in an exemplary embodiment the fiber filtration layer 12 is formedfrom fibers having an average fiber diameter that is less than or equalto about 10 microns, less than or equal to about 8 microns, less thanabout 5 microns, less than about 4 microns, less than about 3 microns,less than about 2 microns, less than about 1.6 microns, less than about1.2 microns, less than about 1 micron, or less than about 0.8 microns.In certain embodiments, the fiber filtration layer has an average fiberdiameter of at least about 0.5 microns, at least about 0.8 microns, atleast about 1 micron, at least about 1.2 microns, at least about 1.6microns, at least about 2 microns, at least about 3 microns, at leastabout 4 microns, at least about 5 microns, or at least about 8 microns.Combinations of the above referenced ranges are also possible (e.g.,between about 0.5 microns and about 10 microns, between about 1 micronand about 5 microns, between about 1.6 microns and about 3 microns).Other ranges are also possible. The average diameter of a fiber can bedetermined, for example, by scanning electron microscopy.

Various materials can also be used to form the fibers, includingsynthetic and non-synthetic materials. In one exemplary embodiment, thefiber filtration layer 12, and any additional filtration layer(s), isformed from meltblown fibers. Certain suitable meltblown processes havebeen described in commonly-owned U.S. Pat. No. 8,608,817, which isincorporated herein by reference in its entirety. In some embodiments,the fiber filtration layer may be formed by wet laid techniques, airlaid techniques, electrospinning, spunbonding, centrifugal spinning orcarding. Exemplary materials include, by way of non-limiting example,polyolefins, such as polypropylene and polyethylene; polyesters, such aspolybutylene terephthalate and polyethylene terephthalate; polyamides,such as Nylon; polycarbonate; polyphenylene sulfide; polystyrene; andpolyurethane.

The fiber filtration layer may include a suitable percentage ofsynthetic fibers. For example, in some embodiments, the weightpercentage of synthetic fibers in the filtration layer may be betweenabout 50 wt % and about 100 wt % of all fibers in the filtration layer.In some embodiments, the weight percentage of synthetic fibers in thefiltration layer may be greater than or equal to about 50 wt %, greaterthan or equal to about 60 wt %, greater than or equal to about 70 wt %,greater than or equal to about 80 wt %, greater than or equal to about90 wt %, or greater than or equal to about 95 wt %. In some embodiments,the weight percentage of the synthetic fibers in the filtration layermay be less than or equal to about 100 wt %, less than or equal to about95 wt %, less than or equal to about 90 wt %, less than or equal toabout 80 wt %, less than or equal to about 70 wt %, or less than orequal to about 50 wt %. Combinations of the above-referenced ranges arealso possible (e.g., a weight percentage of greater than or equal toabout 90 wt % and less than or equal to about 100 wt %). Other rangesare also possible. In some embodiments, a filtration layer includes 100wt % of synthetic fibers. In some embodiments, a filtration layerincludes the above-noted ranges of synthetic fibers with respect to thetotal weight of the filtration layer (e.g., including any resins). Insome embodiments, a combination of filtration layers may have apercentage of synthetic fibers in one or more of the above-referencedranges. Additionally, in embodiments in which more than one filtrationlayers are present in a media, each filtration layer may have apercentage of synthetic fibers having one or more of theabove-referenced ranges. In another embodiment, the above-referencedranges of fibers may apply to the entire filter media (which may includemultiple filtration layers). The remaining fibers of the filtrationlayer and/or filter media may be non-synthetic fibers, such as glassfibers, glass wool fibers, and/or cellulose pulp fibers (e.g., wood pulpfibers).

In some embodiments, the fiber filtration layer 12 may include glassfibers (e.g., microglass fibers, chopped strand glass fibers, or acombination thereof). The type and size of glass fiber can also vary,but in an exemplary embodiment, the fiber is a microglass fiber, such asA-type or E-type glass fibers made using a rotary or flame attenuationprocess and having an average fiber diameter in the range of about 0.2μm to 5 μm. Microglass fibers and chopped strand glass fibers are knownto those of ordinary skill in the art. One of ordinary skill in the artis able to determine whether a glass fiber is microglass or choppedstrand by observation (e.g., optical microscopy, electron microscopy).Microglass fibers may also have chemical differences from chopped strandglass fibers. In some cases, though not required, chopped strand glassfibers may contain a greater content of calcium or sodium thanmicroglass fibers. For example, chopped strand glass fibers may be closeto alkali free with high calcium oxide and alumina content. Microglassfibers may contain 10-15% alkali (e.g., sodium, magnesium oxides) andhave relatively lower melting and processing temperatures. The termsrefer to the technique(s) used to manufacture the glass fibers. Suchtechniques impart the glass fibers with certain characteristics. Ingeneral, chopped strand glass fibers are drawn from bushing tips and cutinto fibers in a process similar to textile production. Chopped strandglass fibers are produced in a more controlled manner than microglassfibers, and as a result, chopped strand glass fibers will generally haveless variation in fiber diameter and length than microglass fibers.Microglass fibers are drawn from bushing tips and further subjected toflame blowing or rotary spinning processes. In some cases, finemicroglass fibers may be made using a remelting process. In thisrespect, microglass fibers may be fine or coarse. As used herein, finemicroglass fibers are less than or equal to 1 micron in diameter andcoarse microglass fibers are greater than or equal to 1 micron indiameter.

The microglass fibers may have small diameters. For instance, in someembodiments, the average diameter of the microglass fibers may be lessthan or equal to about 10 microns, less than or equal to about 9microns, less than or equal to about 7 microns, less than or equal toabout 5 microns, less than or equal to about 3 microns, or less than orequal to about 1 micron. In some instances, the microglass fibers mayhave an average fiber diameter of greater than or equal to about 0.1microns, greater than or equal to about 0.3 microns, greater than orequal to about 1 micron, greater than or equal to about 3 microns, orgreater than or equal to about 7 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0.1 microns and less than or equal to about 10 microns, greaterthan or equal to about 0.1 microns and less than or equal to about 5microns, greater than or equal to about 0.3 microns and less than orequal to about 3 microns). Other values of average fiber diameter arealso possible. Average diameter distributions for microglass fibers aregenerally log-normal. However, it can be appreciated that microglassfibers may be provided in any other appropriate average diameterdistribution (e.g., Gaussian distribution).

In some embodiments, the average length of microglass fibers may be lessthan or equal to about 10 mm, less than or equal to about 10 mm, lessthan or equal to about 8 mm, less than or equal to about 6 mm, less thanor equal to about 5 mm, less than or equal to about 4 mm, less than orequal to about 3 mm, or less than or equal to about 2 mm. In certainembodiments, the average length of microglass fibers may be greater thanor equal to about 1 mm, greater than or equal to about 2 mm, greaterthan or equal to about 4 mm, greater than or equal to about 5 mm,greater than equal to about 6 mm, or greater than or equal to about 8mm. Combinations of the above referenced ranges are also possible (e.g.,microglass fibers having an average length of greater than or equal toabout 4 mm and less than about 6 mm). Other ranges are also possible.

In general, chopped strand glass fibers may have an average fiberdiameter that is greater than the diameter of the microglass fibers. Forinstance, in some embodiments, the average diameter of the choppedstrand glass fibers may be greater than or equal to about 5 microns,greater than or equal to about 7 microns, greater than or equal to about9 microns, greater than or equal to about 11 microns, or greater than orequal to about 20 microns. In some instances, the chopped strand glassfibers may have an average fiber diameter of less than or equal to about30 microns, less than or equal to about 25 microns, less than or equalto about 15 microns, less than or equal to about 12 microns, or lessthan or equal to about 10 microns. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 5 micronsand less than or equal to about 12 microns). Other values of averagefiber diameter are also possible. Chopped strand diameters tend tofollow a normal distribution. Though, it can be appreciated that choppedstrand glass fibers may be provided in any appropriate average diameterdistribution (e.g., Gaussian distribution).

In some embodiments, chopped strand glass fibers may have a length inthe range of between about 3 mm and about 25 mm (e.g., about 6 mm, orabout 12 mm). In some embodiments, the average length of chopped strandglass fibers may be less than or equal to about 25 mm, less than orequal to about 20 mm, less than or equal to about 15 mm, less than orequal to about 12 mm, less than or equal to about 10 mm, less than orequal to about 7 mm, or less than or equal to about 5 mm. In certainembodiments, the average length of chopped strand glass fibers may begreater than or equal to about 3 mm, greater than or equal to about 5mm, greater than or equal to about 10 mm, greater than or equal to about12 mm, greater than equal to about 15 mm, or greater than or equal toabout 20 mm. Combinations of the above referenced ranges are alsopossible (e.g., chopped strand glass fibers having an average length ofgreater than or equal to about 3 mm and less than about 25 mm). Otherranges are also possible.

It should be appreciated that the above-noted dimensions are notlimiting and that the microglass and/or chopped strand fibers, as wellas the other fibers described herein, may also have other dimensions.

In some embodiments, the average diameter of the glass fibers (e.g.,regardless of whether the glass fibers are microglass, chopped strand,or another type) in the fiber filtration layer may be greater than orequal to about 1.5 microns, greater than or equal to about 2 microns,greater than or equal to about 2.5 microns, greater than or equal toabout 3 microns, greater than or equal to about 4.5 microns, greaterthan or equal to about 5 microns, greater than or equal to about 6microns, greater than or equal to about 7 microns, or greater than orequal to about 9 microns. In some instances, the average diameter of theglass fibers in the fiber filtration layer may have an average fiberdiameter of less than or equal to about 10 microns, less than or equalto about 9 microns, less than or equal to about 7 microns, less than orequal to about 6 microns, less than or equal to about 5 microns, lessthan or equal to about 4.5 microns, less than or equal to about 3microns, less than or equal to about 2.5 microns, or less than or equalto about 2 microns. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 1.5 microns and less thanor equal to about 10 microns, greater than or equal to about 2 micronsand less than or equal to about 9 microns, greater than or equal toabout 2 microns and less than or equal to about 5 microns, greater thanor equal to about 2.5 microns and less than or equal to about 4.5microns).

In some embodiments, the average length of the glass fibers in the fiberfiltration layer (e.g., regardless of whether the glass fibers aremicroglass, chopped strand, or another type) may be less than or equalto about 25 mm, less than or equal to about 20 mm, less than or equal toabout 15 mm, less than or equal to about 12 mm, less than or equal toabout 10 mm, less than or equal to about 8 mm, less than or equal toabout 5 mm, less than or equal to about 3 mm, or less than or equal toabout 1 mm. In certain embodiments, the average length of the glassfibers in the fiber filtration layer may be greater than or equal toabout 0.05 mm, greater than or equal to about 0.1 mm, greater than orequal to about 0.3 mm, greater than or equal to about 0.5 mm, greaterthan equal to about 1 mm, greater than or equal to about 5 mm, greaterthan equal to about 10 mm, greater than or equal to about 15 mm, greaterthan equal to about 20 mm, greater than or equal to about 30 mm, orgreater than or equal to about 40 mm. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal toabout 1 mm and less than about 25 mm, greater than or equal to about 0.3mm and less than about 20 mm, greater than or equal to about 0.1 mm andless than about 12 mm, greater than or equal to about 0.2 mm and lessthan about 6 mm, greater than or equal to about 0.5 mm and less thanabout 3 mm). Other ranges are also possible.

The resulting fiber filtration layer 12, as well as any additionalfiltration layer(s), can also have a variety of thicknesses, airpermeabilities, basis weights, and filtration efficiencies dependingupon the requirements of a desired application.

In one exemplary embodiment, the fiber filtration layer 12, as measuredin a planar configuration, has a thickness in the range of about 6 milsto 22 mils; for example, between about 10 mils and about 18 mils, orbetween about 12 mils to 16 mils. Thickness, as referred to herein, isdetermined according to the Edana WSP 120.1 Standard on a planar layerunder approximately 1 ounce load per square foot. Additionally, inembodiments in which more than one filtration layers are present in amedia, each filtration layer may have a thickness having one or more ofthe above-referenced ranges.

The fiber filtration layer may have an air permeability in the range ofabout 30 CFM to 150 CFM. For example, the air permeability may be atleast about 30 CFM, at least about 50 CFM, at least about 65 CFM, atleast about 75 CFM, at least about 100 CFM, or at least about 125 CFM.In some embodiments, the air permeability of the fiber filtration layermay be less than or equal to about 150 CFM, less than or equal to about125 CFM, less than or equal to about 100 CFM, less than or equal toabout 75 CFM, less than or equal to about 65 CFM, or less than or equalabout 50 CFM. Combinations of the above-referenced ranges are alsopossible (e.g., between about 30 CFM to 150 CFM, between about 65 CFM to100 CFM). Other ranges are also possible. As determined herein, the airpermeability is measured according to ASTM D737-04 (2012). The airpermeability of a filtration layer or filter media is an inversefunction of flow resistance and can be measured with a FrazierPermeability Tester. The Frazier Permeability Tester measures the volumeof air per unit of time that passes through a unit area of sample at afixed differential pressure across the sample. Permeability can beexpressed in cubic feet per minute per square foot at a 0.5 inch waterdifferential.

Support Layers

As also indicated above, the filter media 10 can include at least onesupport layer. In an exemplary embodiment, the filter media 10 includesa downstream support layer 14 disposed on the air outflow side O of thefiber filtration layer 12 and that is effective to hold the fiberfiltration layer 12 in the waved configuration. The filter media 10 canalso include an upstream support layer 16 that is disposed on the airentering side I of the fiber filtration layer 12 opposite to thedownstream support layer 14. The upstream support layer 16 can likewisehelp maintain the fiber filtration layer 12 in a waved configuration. Asindicated above, a person skilled in the art will appreciate that thefilter media 10 can include any number of layers, and it need notinclude two support layers, or a top layer. In certain exemplaryembodiments, the filter media 10 can be formed from a fiber filtrationlayer 12 and a single, adjacent support layer 14 or 16. In otherembodiments, the filter media can include any number of additionallayers arranged in various configurations. The particular number andtype of layers will depend on the intended use of the filter media.

The support layers 14, 16 can be formed from a variety of fibers typesand sizes. In an exemplary embodiment, the downstream support layer 14is formed from fibers having an average fiber diameter that is greaterthan or equal to an average fiber diameter of the fiber filtration layer12, the upstream support layer 16, and the top layer 18, if provided. Insome cases, the upstream support layer 16 is formed from fibers havingan average fiber diameter that is less than or equal to an average fiberdiameter of the downstream support layer 14, but that is greater than anaverage fiber diameter of the fiber filtration layer 12 and the toplayer 18. In certain exemplary embodiments, the downstream support layer14 and/or the upstream support layer 16 can be formed from fibers havingan average fiber diameter in the range of about 10 μm to 32 μm, or 12 μmto 32 μm. For example, the average fiber diameter of the downstreamsupport layer and/or the upstream support layer may be in the range ofabout 18 μm to 22 μm. In some cases, the downstream and/or the upstreamsupport layer may comprise relatively finer fibers than traditionalsupport layers. For example, in some embodiments, the finer downstreamand/or finer upstream support layer can be formed from fibers having anaverage fiber diameter in the range of about 9 μm to 18 μm. For example,the finer downstream and/or finer upstream support layer average fiberdiameter may be in the range of about 12 μm to 15 μm.

The fibers of the support layer (e.g., the downstream support layer, theupstream support layer) may have an average fiber length of, forexample, between about 1.0 inches and about 3.0 inches (e.g., betweenabout 1.5 inches and about 2 inches). In some embodiments, the fibers ofthe support layer may have an average fiber length of less than or equalto about 3 inches, less than or equal to about 2.5 inches, less than orequal to about 2 inches, less than or equal to about 1.5 inch, or lessthan or equal to about 1.1 inches. In some embodiments, the fibers ofthe support layer may have an average fiber length of greater than orequal to about 1 inch, greater than or equal to about 1.5 inches,greater than or equal to about 2.0 inches, or greater than or equal toabout 2.5. Combinations of the above referenced ranges are also possible(e.g., fibers having an average fiber length of greater than or equal toabout 1.5 inches and less than about 2 inches). Other ranges are alsopossible.

Various materials can also be used to form the fibers of the supportlayers 14, 16, including synthetic and non-synthetic materials. In oneexemplary embodiment, the support layers 14, 16 are formed from staplefibers, and in particular from a combination of binder fibers andnon-binder fibers. One suitable fiber composition is a blend of at leastabout 20% binder fiber and a balance of non-binder fiber. A variety oftypes of binder and non-binder fibers can be used to form the media ofthe present invention. The binder fibers can be formed from any materialthat is effective to facilitate thermal bonding between the layers, andwill thus have an activation temperature that is lower than the meltingtemperature of the non-binder fibers. The binder fibers can bemonocomponent fibers or any one of a number of bicomponent binderfibers. In one embodiment, the binder fibers can be bicomponent fibers,and each component can have a different melting temperature. Forexample, the binder fibers can include a core and a sheath where theactivation temperature of the sheath is lower than the meltingtemperature of the core. This allows the sheath to melt prior to thecore, such that the sheath binds to other fibers in the layer, while thecore maintains its structural integrity. This may be particularlyadvantageous in that it creates a more cohesive layer for trappingfiltrate. The core/sheath binder fibers can be concentric ornon-concentric, and exemplary core/sheath binder fibers can include thefollowing: a polyester core/copolyester sheath, a polyestercore/polyethylene sheath, a polyester core/polypropylene sheath, apolypropylene core/polyethylene sheath, a polyamide core/polyethylenesheath, and combinations thereof. Other exemplary bicomponent binderfibers can include split fiber fibers, side-by-side fibers, and/or“island in the sea” fibers.

The non-binder fibers can be synthetic and/or non-synthetic, and in anexemplary embodiment the non-binder fibers can be about 100 percentsynthetic. In general, synthetic fibers are preferred over non-syntheticfibers for resistance to moisture, heat, long-term aging, andmicrobiological degradation. Exemplary synthetic non-binder fibers caninclude polyesters, acrylics, polyolefins, nylons, rayons, andcombinations thereof. Alternatively, the non-binder fibers used to formthe media can include non-synthetic fibers such as glass fibers, glasswool fibers, cellulose pulp fibers, such as wood pulp fibers, andcombinations thereof.

The support layer may include a suitable percentage of synthetic fibers.For example, in some embodiments, the weight percentage of syntheticfibers in the support layer may be between about 80 wt % and about 100wt % of all fibers in the support layer. In some embodiments, the weightpercentage of synthetic fibers in the support layer may be greater thanor equal to about 80 wt %, greater than or equal to about 90 wt %, orgreater than or equal to about 95 wt %. In some embodiments, the weightpercentage of the synthetic fibers in the support layer may be less thanor equal to about 100 wt %, less than or equal to about 95 wt %, lessthan or equal to about 90 wt %, or less than or equal to about 85 wt %.Combinations of the above-referenced ranges are also possible (e.g., aweight percentage of greater than or equal to about 80 wt % and lessthan or equal to about 100 wt %). Other ranges are also possible. Insome embodiments, a support layer includes 100 wt % of synthetic fibers.In some embodiments, a support layer includes the above-noted ranges ofsynthetic fibers with respect to the total weight of the support layer(e.g., including any resins). Additionally, in embodiments in which morethan one filtration layers are present in a media, each filtration layerand/or support layer may have a percentage of synthetic fibers havingone or more of the above-referenced ranges. In other embodiments, theabove-referenced ranges of fibers may apply to the entire filter media(which may include multiple filtration layers). The remaining fibers ofthe filtration layer and/or filter media may be non-synthetic fibers,such as glass fibers, glass wool fibers, and/or cellulose pulp fibers(e.g., wood pulp fibers).

The support layers 14, 16 can also be formed using various techniquesknown in the art, including meltblowing, wet laid techniques, air laidtechniques, carding, electrospinning, and spunbonding. In an exemplaryembodiment, however, the support layers 14, 16 are carded or airlaidwebs. The resulting layers 14, 16 can also have a variety ofthicknesses, air permeabilities, and basis weights depending upon therequirements of a desired application. In one exemplary embodiment, thedownstream support layer 14 and the upstream support layer 16, asmeasured in a planar configuration, each have a thickness in the rangeof about 8 mil to 30 mil (e.g., between about 12 mil to 20 mil), a basisweight in the range of about 10 gsm to 99 gsm (e.g., between about 22gsm and about 99 gsm, between about 33 gsm and 70 gsm), and a mean flowpore size in the range of about 30 microns to 150 microns (e.g., betweenabout 50 microns and about 120 microns).

For example, In some embodiments, the support layer(s) each have athickness of at least about 8 mil, at least about 10 mil, at least about12 mil, at least about 15 mil, at least about 20 mil, or at least about25 mil. In certain embodiments, the support layer(s) may have athickness of less than or equal to about 30 mil, less than or equal toabout 25 mil, less than or equal to about 20 mil, less than or equal toabout 15 mil, less than or equal to about 12 mil, or less than or equalto about 10 mil. Combinations of the above-referenced ranges are alsopossible (e.g., between about 8 mil and about 30 mil, between about 12mil and about 20 mil). Other ranges are also possible. Thickness of thesupport layer(s) is determined as described herein according to theEdana WSP 120.1 Standard on a planar layer under approximately 1 ounceload per square foot.

In certain embodiments, the support layer(s) each have a basis weight ofat least about 10 gsm, at least about 20 gsm, at least about 22 gsm, atleast about 33 gsm, at least about 50 gsm, at least about 60 gsm, atleast about 70 gsm, at least about 80 gsm, or at least about 90 gsm. Insome embodiments, the support layer(s) each have a basis weight of lessthan or equal to about 99 gsm, less than or equal to about 90 gsm, lessthan or equal to about 80 gsm, less than or equal to about 70 gsm, lessthan or equal to about 60 gsm, less than or equal to about 50 gsm, lessthan or equal to about 33 gsm, less than or equal to about 22 gsm, orless than or equal to about 22 gsm. Combinations of the above-referencedranges are also possible (e.g., between about 10 gsm and about 99 gsm,between about 33 gsm and about 70 gsm). Other ranges are also possible.As described herein, the basis weight of the support layer(s) ismeasured according to the Edana WSP 130.1 Standard.

In some embodiments, the support layer(s) have a mean flow pore size ofat least about 30 microns, at least about 40 microns, at least about 50microns, at least about 75 microns, at least about 100 microns, or atleast about 120 microns. In certain embodiments, the support layer(s)have a mean flow pore size of less than or equal to about 150 microns,less than or equal to about 120 microns, less than or equal to about 100microns, less than or equal to about 75 microns, less than or equal toabout 50 microns, or less than or equal to about 40 microns.Combinations of the above-referenced ranges are also possible (e.g.,between about 30 microns to 150 microns, between about 50 microns andabout 120 microns). Other ranges are also possible. Mean flow pore sizemay be determined by a capillary flow porometer, as described above.

Outer or Cover Layer

As previously indicated, the filter media 10 can also optionally includeone or more outer or cover layers disposed on the air entering side Iand/or the air outflow side O. FIG. 1A illustrates a top layer 18disposed on the air entering side I of the filter media 10. The toplayer 18 can function as a dust loading layer and/or it can function asan aesthetic layer. In an exemplary embodiment, the top layer 18 is aplanar layer that is mated to the filter media 10 after the fiberfiltration layer 12 and the support layers 14, 16 are waved. The toplayer 18 thus provides a top surface that is aesthetically pleasing. Thetop layer 18 can be formed from a variety of fiber types and sizes, butin an exemplary embodiment the top layer 18 is formed from fibers havingan average fiber diameter that is less than an average fiber diameter ofthe upstream support layer 16 disposed immediately downstream of the toplayer 18, but that is greater than an average fiber diameter of thefiber filtration layer 12. In certain exemplary embodiments, the toplayer 18 is formed from fibers having an average fiber diameter in therange of about 5 μm to 20 μm. As a result, the top layer 18 can functionas a dust holding layer without affecting the alpha value of the filtermedia 10, as will be discussed in more detail below.

As shown in FIG. 1B, the filter media 10B can alternatively or inaddition include a bottom layer 18B disposed on the air outflow side Oof the filter media 10B. The bottom layer 18B can function asstrengthening component that provides structural integrity to the filtermedia 10B to help maintain the waved configuration. The bottom layer 18Bcan also function to offer abrasion resistance. This may be particularlydesirable in ASHRAE bag applications where the outermost layer issubject to abrasion during use. The bottom layer 18B can have aconfiguration similar to the top layer 18, as discussed above. In anexemplary embodiment, however, the bottom layer 18B is the coarsestlayer, i.e., it is formed from fibers having an average fiber diameterthat is greater than an average fiber diameter of fibers forming all ofthe other layers of the filter media. One exemplary bottom layer is aspunbond layer, however various other layers can be used having variousconfigurations.

Various materials can also be used to form the fibers of the outer orcover layer, including synthetic and non-synthetic materials. In oneexemplary embodiment, the outer or cover layer, e.g., top layer 18and/or bottom layer 18B, is formed from staple fibers, and in particularfrom a combination of binder fibers and non-binder fibers. One suitablefiber composition is a blend of at least about 20% binder fiber and abalance of non-binder fiber. A variety of types of binder and non-binderfibers can be used to form the media of the present invention, includingthose previously discussed above with respect to the support layers 14,16.

The outer or cover layer, e.g., top layer 18 and/or any bottom layer,can also be formed using various techniques known in the art, includingmeltblowing, wet laid techniques, air laid techniques, carding,electrospinning, and spunbonding. In an exemplary embodiment, however,the top layer 18 is an airlaid layer and the bottom layer 18B is aspunbond layer. The resulting layer can also have a variety ofthicknesses, air permeabilities, and basis weights depending upon therequirements of a desired application. In one exemplary embodiment, theouter or cover layer, as measured in a planar configuration, has athickness in the range of about 2 mil to 50 mil, an air permeability inthe range of about 100 CFM to 1200 CFM, and a basis weight in the rangeof about 10 gsm to 50 gsm.

A person skilled in the art will appreciate that, while FIG. 1Aillustrates a four layer filter media, the media can include any numberof layers in various configurations. Various layers can be added toenhance filtration, to provide support, to alter structure, or forvarious other purposes. By way of non-limiting example, the filter mediacan include various spunbond, wetlaid cellulose, drylaid syntheticnonwoven, wetlaid synthetic, and wetlaid microglass layers.

Method of Manufacturing

Some or all of the layers can be formed into a waved configuration usingvarious manufacturing techniques, but in an exemplary embodiment thefiltration layer 12 (e.g., fine fiber), any additional filtrationlayers, and at least one of the support layers 14, 16, are positionedadjacent to one another in a desired arrangement from air entering sideto air outflow side, and the combined layers are conveyed between firstand second moving surfaces that are traveling at different speeds, suchas with the second surface traveling at a speed that is slower than thespeed of the first surface. A suction force, such as a vacuum force, canbe used to pull the layers toward the first moving surface, and thentoward the second moving surface as the layers travel from the first tothe second moving surfaces. The speed difference causes the layers toform z-direction waves as they pass onto the second moving surface, thusforming peaks and troughs in the layers. The speed of each surface canbe altered to obtain the desired number of waves per inch. The distancebetween the surfaces can also be altered to determine the amplitude ofthe peaks and troughs, and in an exemplary embodiment the distance isadjusted between 0.025″ to 4″. For example, the amplitude of the peaksand waves may be between about 0.1″ to 4.0″, e.g., between about 0.1″ to1.0″, between about 0.1″ to 2.0″, or between about 3.0″ to 4.0″. Forcertain applications, the amplitude of the peaks and waves may bebetween about 0.1″ and 1.0″, between about 0.1″ and 0.5″, or betweenabout 0.1″ and 0.3″. The properties of the different layers can also bealtered to obtain a desired filter media configuration. In an exemplaryembodiment the filter media has about 2 to 6 waves per inch, with aheight (overall thickness) in the range of about 0.025″ to 2″, howeverthis can vary significantly depending on the intended application. Forinstance, in other embodiments, the filter media may have about 2 to 4waves per inch, e.g., about 3 waves per inch. The overall thickness ofthe media may be between about 0.025″ to 4.0″, e.g., between about 0.1″to 1.0″, between about 0.1″ to 2.0″ or between about 3.0″ to 4.0″. Forcertain applications, the overall thickness of the media may be betweenabout 0.1″ and 0.5″, or between about 0.1″ and 0.3″. As shown in FIG.1A, a single wave W extends from the middle of one peak to the middle ofan adjacent peak. Thickness of the (waved) filter media can bedetermined as described above according to the Edana WSP 120.1 Standardunder approximately 1 ounce load per 1 square inch pressure foot.

In the embodiment shown in FIG. 1A, when the fiber filtration layer 12and the support layers 14, 16 are waved, the resulting fiber filtrationlayer 12 will have a plurality of peaks P and troughs T on each surface(i.e., air entering side I and air outflow side O) thereof, as shown inFIG. 1C. The support layers 14, 16 will extend across the peaks P andinto the troughs T so that the support layers 14, 16 also have wavedconfigurations. A person skilled in the art will appreciate that a peakP on the air entering side I of the fiber filtration layer 12 will havea corresponding trough T on the air outflow side O. Thus, the downstreamsupport layer 14 will extend into a trough T, and exactly opposite thatsame trough T is a peak P, across which the upstream support layer 16will extend. Since the downstream support layer 14 extends into thetroughs T on the air outflow side O of the fiber filtration layer 12,the downstream coarse layer 14 will maintain adjacent peaks P on the airoutflow side O at a distance apart from one another and will maintainadjacent troughs T on the air outflow side O at a distance apart fromone another. The upstream support layer 16, if provided, can likewisemaintain adjacent peaks P on the air entering side I of the fiberfiltration layer 12 at a distance apart from one another and canmaintain adjacent troughs T on the air entry side I of the fiberfiltration layer 12 at a distance apart from one another. As a result,the fiber filtration layer 12 has a surface area that is significantlyincreased, as compared to a surface area of the fiber filtration layerin the planar configuration. In certain exemplary embodiments, thesurface area in the waved configuration is increased by at least about50%, and in some instances as much as 120%, as compared to the surfacearea of the same layer in a planar configuration.

In embodiments in which the upstream and/or downstream support layershold the fiber filtration layer in a waved configuration, it may bedesirable to reduce the amount of free volume (e.g., volume that isunoccupied by any fibers) in the troughs. That is, a relatively highpercentage of the volume in the troughs may be occupied by the supportlayer(s) to give the fiber layer structural support. For example, atleast 95% or substantially all of the available volume in the troughsmay be filled with the support layer and the support layer may have asolidity ranging between about 1% to 90%, between about 1% to 50%,between about 10% to 50%, or between about 20% to 50%. Additionally, asshown in the exemplary embodiments of FIG. 1A, the extension of thesupport layer(s) across the peaks and into the troughs may be such thatthe surface area of the support layer in contact with a top layer 18A issimilar across the peaks as it is across the troughs. Similarly, thesurface area of the support layer in contact with a bottom layer 18B(FIG. 1B) may be similar across the peaks as it is across the troughs.For example, the surface area of the support layer in contact with a topor bottom layer across a peak may differ from the surface area of thesupport layer in contact with the top or bottom layer across a trough byless than about 70%, less than about 50%, less than about 30%, less thanabout 20%, less than about 10%, or less than about 5%.

In certain exemplary embodiments, the downstream and/or upstream supportlayers 14, 16 can have a fiber density that is greater at the peaks thanit is in the troughs; and, in some embodiments, a fiber mass that isless at the peaks than it is in the troughs. This can result from thecoarseness of the downstream and/or upstream support layers 14, 16relative to the fiber filtration layer 12. In particular, as the layersare passed from the first moving surface to the second moving surface,the relatively fine nature of the fiber filtration layer 12 will allowthe downstream and/or upstream support layers 14, 16 to conform aroundthe waves formed in the fiber filtration layer 12. As the support layers14, 16 extend across a peak P, the distance traveled will be less thanthe distance that each layer 14, 16 travels to fill a trough. As aresult, the support layers 14, 16 will compact at the peaks, thus havingan increased fiber density at the peaks as compared to the troughs,through which the layers will travel to form a loop-shapedconfiguration.

Once the layers are formed into a waved configuration, the waved shapecan be maintained by activating the binder fibers to effect bonding ofthe fibers. A variety of techniques can be used to activate the binderfibers. For example, if bicomponent binder fibers having a core andsheath are used, the binder fibers can be activated upon the applicationof heat. If monocomponent binder fibers are used, the binder fibers canbe activated upon the application of heat, steam and/or some other formof warm moisture. A top layer 18 (FIG. 1A) and/or bottom layer 18B (FIG.1B) can also be positioned on top of the upstream support layer 16 (FIG.1A) or on the bottom of the downstream support layer 14B (FIG. 1B),respectively, and mated, such as by bonding, to the upstream supportlayer 16 or downstream support layer 14B simultaneously or subsequently.A person skilled in the art will also appreciate that the layers canoptionally be mated to one another using various techniques other thanusing binder fibers. The layers can also be individually bonded layers,and/or they can be mated, including bonded, to one another prior tobeing waved.

A saturant can also optionally be applied to the material prior todrying the material. A variety of saturants can be used with the mediaof the present invention to facilitate the forming of the layers at atemperature that is less than the melting temperature of the fibers.Exemplary saturants can include phenolic resins, melamine resins, urearesins, epoxy resins, polyacrylate esters, polystyrene/acrylates,polyvinyl chlorides, polyethylene/vinyl chlorides, polyvinyl acetates,polyvinyl alcohols, and combinations and copolymers thereof that arepresent in an aqueous or organic solvent.

In some embodiments, the resulting media can also have a gradient in atleast one, and optionally all, of the following properties: binder andnon-binder fibers composition, fiber diameter, solidity, basis weight,and saturant content. For example, in one embodiment, the media can havea lightweight, lofty, coarse-fibered, lightly bonded and lightlysaturated sheet upstream, and a heavier, denser, fine-fibered, heavilybonded and heavily saturated sheet downstream. This allows the coarserparticles to be trapped in the upstream layer, preventing earlysaturation of the bottom layer. In other embodiments, the upstream-mostlayer can be lighter and/or loftier than the downstream-most layer. Thatis, the upstream layer can have a solidity (e.g., the solid volumefraction of fibers in the layer) and a basis weight that is less thanthat of the downstream layer. Additionally, in embodiments where thefilter media includes a saturant, the media can have a gradient withrespect to the amount of saturant in the upstream-most anddownstream-most layers. One skilled in the art will appreciate thevariety of properties that the layers of the media can have.

An electrostatic charge can also optionally be imparted to the filtermedia, or to various layers of the media, to form an electret fiberlayer. For example, a charge may be imparted to a fiber filtration layerprior to joining with one or more support layers. In another embodiment,a charge is imparted to a filter media including more than one layer,e.g., a fiber filtration layer and one or more support layers. Dependingon the materials used to form each of the layers, the amount of charge,and the method of charging, the charge may either remain in one or moreof the layers or dissipate after a short period of time (e.g., withinhours). A variety of techniques are well known to impart a permanentdipole to the polymer web in order to form electret filter media.Charging can be effected through the use of AC and/or DC coronadischarge units and combinations thereof. The particular characteristicsof the discharge are determined by the shape of the electrodes, thepolarity, the size of the gap, and the gas or gas mixture. Charging canalso be accomplished using other techniques, including friction-basedcharging techniques.

In some embodiments, the fiber filtration layer may be made hydrophobicor hydrophilic. In some cases, the hydrophilicity of a filtration layermay alter the change in pressure drop of an NaCl loaded media ascompared to unloaded media. In some cases, the fiber filtration layermay be hydrophobic. In certain embodiments, the fiber filtration layermay be hydrophilic. Those skilled in the art would be capable ofselecting suitable methods for making the fiber filtration layerhydrophobic or hydrophilic including, but not limited to, the additionof a hydrophobic or a hydrophilic coating, inclusion of additives (e.g.,during extrusion of the fibers), and/or selecting of hydrophobic orhydrophilic fiber materials. In some cases, the fibers of the supportlayer may also be selectively made hydrophobic or hydrophilic. Forexample, such support layers could be carded or airlaid webs withtopical finishes applied to the fibers before processing, and/or thefibers could be selected based on their hydrophobic or hydrophilicproperties.

The filter media can also be pleated after it is formed into the wavedconfiguration, and various exemplary configurations will be discussed inmore detail below. A person skilled in the art will appreciate thatvirtually any pleating technique known in the art can be used to pleatthe waved filter media. Typically, a filter media is pleated by forminga plurality of parallel score lines in the media and forming folds ateach score line.

Filter Media Properties

As indicated above, the properties of the resulting filter media canvary depending on the intended use. In some embodiments, the mean flowpore size of the fiber filtration layer is effective to improve theperformance (e.g., reduced air permeability decrease) of a filter mediain relatively high humidity environments.

In some embodiments, the filter media described herein is classified asa G1, G2, G3, G4, M5, M6, F7, F8, or F9 filter media. The averageefficiency and minimum efficiency ranges for 0.4 micron or larger DEHSparticles for these classifications are listed in Table 1. As statedbelow, the testing is performed until a maximum final pressure drop of250 Pa or 450 Pa, according to the EN779-2012 standard described above.

TABLE 1 Final test pressure Average Average Minimum drop arrestance(A_(m)) efficiency (E_(m)) Efficiency* Group Class Pa of synthetic dust% of 0.4 μm particles % of 0.4 μm particles % Coarse G1 250 50 ≤ A_(m) <65 — — G2 260 65 ≤ A_(m) < 80 — — G3 260 80 ≤ A_(m) < 90 — — G4 260 90 ≤A_(m) — — Medium M5 450 — 40 ≤ E_(m) < 60 — M6 450 — 60 ≤ E_(m) < 80 —Fine F7 450 — 80 ≤ E_(m) < 90 35 F8 450 — 90 ≤ E_(m) < 95 55 F9 450 — 95≤ E_(m) 70

The resulting media can also have a variety of thicknesses, airpermeabilities, basis weights, and initial efficiencies depending uponthe requirements of a desired application. Thickness, as referred toherein, is determined according to the Edana WSP 120.1 Standard using anappropriate caliper gage. Basis weight, as referred to herein, isdetermined according to the Edana WSP 130.1 Standard.

For example, in one embodiment, the resulting media can have a thicknesst_(m), as shown in FIG. 1A, in the range of about 80 mil to 250 mil(e.g., about 140 mil to 180 mil), an amplitude of the peaks and waves ofbetween about 0.025″ to 4″ (e.g., between about 0.1″ to 1.0″, betweenabout 0.1″ to 2.0″, or between about 3.0″ to 4.0″ in some applications,between about 0.1″ and 0.5″, or between about 0.1″ and 0.3″ in otherapplications), and an air permeability in the range of about 30 CFM to400 CFM (e.g., between about 50 CFM to 120 CFM, or between about 70 CFMto 90 CFM). The resulting media can also have a basis weight in therange of about 125 gsm to 250 gsm (e.g., about 150 to 250 gsm, or about135 gm to 160 gsm), and/or a NaCl loading of less than about 25 mm H₂Oafter loading approximately 60 mg/100 cm² of about 0.3 μm particles at5.3 cm/s face velocity (e.g., less than about 20 mm H₂O).

Filter Elements

As previously indicated, the filter media disclosed herein can beincorporated into a variety of filter elements for use in variousapplications, including both liquid and air filtration applications.Exemplary uses include ASHRAE bag filters, pleatable HVAC filters, gasturbine bag filters, liquid bag filter media, dust bag house filters,residential furnace filters, paint spray booth filters, face masks(e.g., surgical face masks and industrial face masks), cabin airfilters, commercial ASHRAE filters, respirator filters, automotive airintake filters, automotive fuel filters, automotive lube filters, roomair cleaner filters and vacuum cleaner exhaust filters. The filterelements can have various configurations, and certain exemplary filterelement configurations are discussed in more detail below. Otherexemplary filter elements include, by way of non-limiting example,radial filter elements that include cylindrical filter media disposedtherein, micron-rater vessel bag filters (also referred to as sockfilters) for liquid filtration, face masks, etc.

Panel Filter

In one exemplary embodiment, the filter media can be used in a panelfilter. In particular, the filter media can include a housing disposedtherearound. The housing can have various configurations, and theparticular configuration can vary based on the intended application. Thehousing may be in the form of a frame that is disposed around theperimeter of the filter media. The frame may have a generallyrectangular configuration such that it surrounds all four sides of agenerally rectangular filter media 10, however the particular shape canvary. The frame can be formed from various materials, includingcardboard, metal, polymers, etc. In certain exemplary embodiments, theframe can have a thickness that is about 12″ or less, or about 2″ orless. In another embodiment, the frame can be formed from the edges ofthe filter media. In particular, a perimeter of the filter media 10′ canbe thermally sealed to form a frame therearound. The panel filter canalso include a variety of other features known in the art, such asstabilizing features for stabilizing the filter media relative to theframe, spacers, etc.

In use, the panel filter element can be used in a variety ofapplications, including commercial and residential HVAC (e.g., furnacefilters); automotive passenger cabin air; automotive air intake; andpaint spray booth filters. The particular properties of the filterelement can vary based on the intended use, but in certain exemplaryembodiments, the filter element has a MERV rating in the range of 7 to20, and may be, for example, greater than about 13, greater than about15, greater than about 17, or greater than about 19. The filter elementmay have a pressure drop in the range of about 0.1″ to 5″ H₂O, e.g.,between about 0.1″ to 1″ H₂O.

Pleated Filter

The waved filter media can also be pleated and used in a pleated filter.As previously discussed, the waved media, or various layers thereof, canbe pleated by forming score lines at a predetermined distance apart fromone another, and folding the media. A person skilled in the art willappreciate, however, that other pleating techniques can be used. Oncethe media is pleated, the media can be incorporated into a housing. Themedia can have any number of pleats depending on the size of the frameand the intended use. In certain exemplary embodiment, the filter mediahas 1-2 pleats per inch, and a pleat height in the range of about 0.75″to 2″. However, some applications utilize peaks having a height up to12″.

In order to facilitate pleating, the filter media can beself-supporting, i.e., it can have a stiffness that allows pleating. Incertain exemplary embodiments, the minimum stiffness of the filter mediais about 200 mg with Gurley Stiffness tester to enable pleating.Alternatively, or in addition, the filter media can include variousstiffening elements (e.g., stabilizing straps, screen backing, and thelike).

In use, the pleated waved filter element can be used in a variety ofapplications, including pleatable HVAC filters, residential furnacefilters, cabin air filters, commercial ASHRAE filters, automotive airintake filters, automotive fuel filters, automotive lube filters, roomair cleaner filters, and vacuum cleaner exhaust filters. The particularproperties of the filter element can vary based on the intended use, butin certain exemplary embodiments, the filter element has a MERV ratingin the range of 7 to 20. For example, the MERV rating may be greaterthan about 13, greater than about 15, greater than about 17, or greaterthan about 19. The filter element may have a pressure drop in the rangeof about 0.1″ to 5″ H₂O, e.g., between about 0.1″ to 1″ H₂O. The filtermedia can also have a thickness before pleating of about 0.5″ of less,and a thickness after pleating of about 2″ or less. However, in certainapplication the thickness after pleating can be up to 12″.

Bag/Pocket Filter

In yet another embodiment, the filter media can be incorporated into abag or pocket filter for use in heating, air conditioning, ventilation,gas turbine filtration, and/or refrigeration; and micron rated liquidfilter bags. The bag or pocket filter can be formed by placing twofilter media together (or folding a single filter media in half), andmating three sides (or two if folded) to one another such that only oneside remains opens, thereby forming a pocket inside the filter. In someembodiments, multiple filter pockets can be attached to a frame to forma filter element. Each pocket can be positioned such that the open endis located in the frame, thus allowing air to flow into each pocket. Theframe can include rectangular rings that extend into and retain eachpocket. A person skilled in the art will appreciate that the frame canhave virtually any configuration, and various mating techniques known inthe art can be used to couple the pockets to the frame. Moreover, theframe can include any number of pockets, but bag filters typicallyinclude between 6 and 10 pockets.

The particular properties of the filter element can vary based on theintended use, but in certain exemplary embodiments, the filter elementhas a MERV rating in the range of about 7 to 20 (e.g., 13 to 20). Forexample, the MERV rating may be greater than about 13, greater thanabout 15, greater than about 17, or greater than about 19. The filterelement may have a pressure drop in the range of about 0.1″ to 5″ H₂O,e.g., between about 0.1″ to 1″ H₂O. The filter media can also have athickness that is about 2″ or less, or about 0.5″ or less, however thethickness can vary depending on the intended application.

By way of non-limiting example, a standard 8 pocket ASHRAE bag filtertypically has a 30″ deep pocket in a 24″×24″ frame, and yields 80 sq.ft. of media. An ASHRAE bag filter having the same dimensions, bututilizing a waved filter media according to the present invention, willyield 176 sq. ft. of media.

Facemask

In yet another embodiment, the filter media can be incorporated into apersonal protective filtration device, such as a facemask, that isdesigned to remove contaminants from breathable air. In one embodiment,the filter media is used to form an industrial facemask designed for usein the workplace. The facemask may include, for example, an outerstructural support layer, a filtration layer, and an inner structuralsupport layer, although any suitable combination of layers can be used.Each of the layers may be charged or uncharged. Each of the layers maybe hydrophobic or hydrophilic. The structural support layers may benonwoven layers that are thermally moldable under suitable conditions,e.g., at a temperature of about 105-110° C. for 6-8 seconds. Thefiltration layers may be formed from meltblown or fiberglass materials.In one set of embodiments, a facemask has a filter area of approximately170 cm², which is standard in the United States, or an area ofapproximately 150 cm², which may be standard in other areas of theworld.

In another embodiment, the filter media is used in a surgical facemask.A surgical facemask includes a personal protective filtration devicetypically worn by medical personnel for two primary reasons: to preventthe transfer of germs from medical personnel to patient (and viceversa), and to protect medical personnel from the strike of insultingbodily fluids. A surgical facemask may include, for example, an outerstructural support layer, a filtration layer, and an inner structuralsupport layer, although any suitable combination of layers can be used.Each of the layers may be charged or uncharged. In some embodiments, thestructural support layers are polypropylene spunbond and the filtrationlayers are formed from meltblown or fiberglass materials. The filtermedia may be folded for larger coverage area, and may include a filterarea of, for example, 200-1000 cm².

The following non-limiting examples serve to further illustrate thepresent invention:

EXAMPLE 1

This example illustrates the importance of mean flow pore size onfiltration performance according to some embodiments described herein.

Samples A-G are melt blown fiber filtration layer samples (in a planarconfiguration without support layer(s)) designed to have a minimum DEHSefficiency of at least 25%). A number of properties of the samples weremeasured and the results are shown in Table 2.

TABLE 2 Mean flow pore size Sample Avg. Basis Weight (gsm) (microns) A9.3 10.43 B 18.6 16.38 C 15.6 12.83 D 14.2 12.54 E 15.8 13.56 F 4.2 6.1G 8.7 10.96

Transition salt load testing was conducted on the samples following theprotocol described above.

FIG. 2A shows a plot of the Resistance (mm H₂O) vs. NaCl loading (gsm)for Samples A and B obtained from the transition salt load testing. Theplot also shows the cake loading lines and initial depth loading linesfor Samples A and B. As described above, the transition salt load isdefined as the value of NaCl load per unit area (gsm) at theintersection of the initial depth loading line and the cake loadingline. Sample A (with a mean flow pore size of 10.43 microns) had atransition salt load of about 1.2, and Sample B (with a mean flow poresize of 16.38 microns) had a transition salt load of about 3.6.

FIG. 2B shows a plot of the transition salt load for Samples A-G as afunction of mean flow pore size. As shown, the samples having a meanflow pore size of greater than 11.5 microns had a significantly highertransition salt load than the samples having a mean flow pore size ofless than 11.5 microns. Higher transition salt loads are generallycorrelated with improved filtration performance in high humidityconditions, as well as standard conditions.

FIG. 2C shows a plot of the slope of the cake loading line versus meanflow pore size for Samples A-G. As shown, the samples having a mean flowpore size of greater than 11.5 microns had lower slopes of the cakeloading line than samples having a mean flow pore size of less than 11.5microns. The lower slopes can lead to higher transition salt loads whichgenerally are correlated with improved high humidity filtrationperformance.

FIGS. 2B-2C demonstrate that fiber filtration layers having a minimumDEHS efficiency of at least 25% and a mean flow pore size of at leastabout 11.5 microns had significantly increased transition salt loads ascompared to fiber filtration layers at this efficiency with less than11.5 micron mean flow pore sizes. Since high transition salt loads aregenerally correlated with improved high humidity performance, the fiberfiltration layers having a mean flow pore size of at least about 11.5microns are expected to have improved filtration performance in highhumidity environments.

FIG. 3A is a plot of the specific natural log of penetration (i.e., thenatural log of the penetration divided by the basis weight) versus meanflow pore size for Samples A-G. The regression curve shown on the plotdemonstrates a relationship between fiber filtration layer mean flowpore size, fiber filtration layer basis weight and penetration.Therefore, there is also a relationship between fiber filtration layermean flow pore size, fiber filtration layer basis weight and efficiency.For example, the following equation has been derived, in part from thelatter relationship, to identify suitable mean pore size and basisweight values needed to obtain a target minimum DEHS efficiency.

${BW} > {- \frac{{MP}^{2\;}\left( {{Ln}\left( {1 - E} \right)} \right)}{6.5}}$where BW is the basis weight of the fiber filtration layer, MP is themean flow pore size, and E is the minimum DEHS efficiency for the fiberfiltration layer that is being targeted.

FIG. 3B is a plot of the basis weight (gsm) versus mean flow pore sizefor Samples A-G. The relationship above is used to define the curvewhich is a boundary of the basis weight and mean flow pore size valuesat which a minimum DEHS efficiency of 35% (to meet F7 classification) ismet. Fiber filtration layers having combinations of basis weight andmean flow pore size that lie on or above the boundary have a minimumDEHS efficiency of 35% or greater. The fiber filtration layers having amean flow pore size of greater than 11.5 microns and lie on or above theboundary also have improved high humidity performance, as noted above.

EXAMPLE 2

This example demonstrates the correlation between performance of afilter media and mean flow pore size under humid conditions.

Filter media samples including a range of mean pore sizes (from about 10microns to 16.5 microns) were tested in a humid environment. The filtermedia samples included a fiber filtration layer between two supportlayers with the combined layers being in a waved configuration. Thetesting followed the protocol described above to measure the percentdecrease in air permeability after humidity loading.

As noted in the protocol described above, the percent decrease in airpermeability after humidity loading is the difference between themaximum air permeability (as measured during the testing) minus theminimum air permeability (as measured during the testing) expressed as apercentage of the maximum air permeability value. FIG. 4 shows a plot ofthe difference versus mean flow pore size. As shown on the plot, formean flow pore sizes greater than about 11.5 microns, the averagedifference was about 44% or less. For mean flow pore sizes less than11.5 microns, the average difference was 46% or greater.

This data shows that filter media including mean flow pore sizes ofgreater than 11.5 microns experience smaller differences between maximumair permeability and minimum air permeability than filter mediaincluding mean flow pore sizes of less than 11.5 microns.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. A filter media, comprising: a fiber filtrationlayer and a support layer that holds the fiber filtration layer in awaved configuration and maintains separation of peaks and troughs ofadjacent waves of the fiber filtration layer, wherein the support layerextends across the peaks and into the troughs to substantially fill thetroughs, wherein the fiber filtration layer has a mean flow pore size ofat least about 11.5 microns and less than or equal to about 45 microns;and wherein the filter media has a minimum DEHS particle filtrationefficiency of at least about 25%.
 2. A filter media as in claim 1,wherein the fiber filtration layer comprises hydrophilic fibers.
 3. Afilter media as in claim 1, wherein the fiber filtration layer compriseshydrophobic fibers.
 4. A filter media as in claim 1, wherein the basisweight of the fiber filtration layer is selected such that:${BW} > \frac{{- {MP}^{a\;}}{\ln\left( {1 - E} \right)}}{b}$ wherein: BWis the basis weight of the fiber filtration layer in grams per squaremeter; MP is the mean pore size of the fiber filtration layer inmicrons; E is the minimum DEHS efficiency of the fiber filtration layerexpressed as a fraction; a is equal to 2; and b is equal to 6.5.
 5. Afilter media as in claim 1, wherein the support layer comprises fibershaving an average fiber diameter of between about 9 microns and about 18microns.
 6. A filter media as in claim 1, wherein the filter mediacomprises a second support layer having an average fiber diameter ofbetween about 9 microns and about 18 microns.
 7. A filter media as inclaim 1, wherein the filter media further comprises at least one coverlayer disposed on the support layer.
 8. A filter media as in claim 1,wherein the fiber filtration layer comprises fibers having an averagefiber diameter of between about 1 micron and about 5 microns.
 9. Afilter media as in claim 1, wherein the fiber filtration layer has abasis weight of greater than or equal to about 10 g/m² and less than orequal to about 40 g/m².
 10. A filter media as in claim 1, wherein thefiber filtration layer has a basis weight of greater than or equal toabout 13 g/m² and less than or equal to about 20 g/m².
 11. A filtermedia as in claim 1, wherein the fiber filtration layer has a slope of acake loading line of between 1 mm H₂O/gsm salt load per sample and about7 mm H₂O/gsm salt load per sample.
 12. A filter media as in claim 1,wherein the fiber filtration layer has a thickness in the range of about6 mils to 22 mils.
 13. A filter media as in claim 1, wherein the fiberfiltration layer has an air permeability in the range of about 30 CFM to150 CFM, as measured according to ASTM F778-88.
 14. A filter media as inclaim 1, wherein the fiber filtration layer has a surface area of atleast about 0.8 grams per square meter.
 15. A filter media as in claim1, wherein the fiber filtration layer has an amplitude of the peaks andtroughs of between about 0.1″ to 4.0″.
 16. A filter media as in claim 1,wherein the filter media has a percent decrease in air permeabilityafter humidity loading of less than or equal to about 45%.
 17. A filtermedia as in claim 1, wherein the filter media has a percent decrease inair permeability after humidity loading of less than or equal to about50%.
 18. A filter media as in claim 1, wherein the fiber filtrationlayer has a solidity between about 1% and about 20%.
 19. A filter mediaas in claim 1, wherein the filter media has a minimum DEHS particlefiltration efficiency of at least about 35%.
 20. A filter media as inclaim 1, wherein the fiber filtration layer in the waved configurationis formed from a fiber layer having a planar configuration and atransition salt load of at least about 3.5 gsm.